login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A287221 Number of twice-crossing partitions on n nodes. 2
0, 0, 0, 0, 8, 42, 168, 760, 2418, 10490, 30842, 131676 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

The meandric numbers A005316 are the numbers of paths which cross themselves 0 times.

This sequence is the number of paths that must cross themselves exactly twice.

LINKS

Table of n, a(n) for n=0..11.

B. W. J. Irwin, On the number of k-crossing partitions

EXAMPLE

a(4) = 8; this is from the partitions

(2,1,4,3), (2,4,3,1),

(3,2,4,1), (3,4,2,1),

(4,1,3,2), (4,2,1,3),

(4,2,3,1), (4,3,1,2).

CROSSREFS

Cf. A005316, A287220.

Sequence in context: A231069 A319235 A256861 * A119965 A229729 A055082

Adjacent sequences:  A287218 A287219 A287220 * A287222 A287223 A287224

KEYWORD

nonn,more

AUTHOR

Benedict W. J. Irwin, May 22 2017

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 29 16:43 EDT 2020. Contains 334704 sequences. (Running on oeis4.)